The present invention relates to an improved process for contact winding a film web onto a winding core to obtain a film roll. More particularly, the present invention relates to a contact winding process in which air layers adjacent the film surface are substantially displaced from the film web immediately prior to winding. The present invention also relates to an apparatus for the wrinkle-free winding of a film web.
The last step in the manufacturing process of films is the winding of the film web into a film roll. This winding step is highly significant. If a film web which is within specification is "incorrectly" wound, damage to the film can result in a possible total loss of the film roll, especially through storage.
An especially important problem within this context is the phenomenon of air entrapment. Enormous amounts of air are entrapped in the winding core during the winding of the film web. A portion of the entrapped air escapes from the winding core during its storage, thereby possibly causing various flaws, such as collapses, gauge bands, and TD lines. These flaws can lead to the complete uselessness of the film roll.
U.S. Pat. No. 4,576,344 discloses a device for winding polyester film webs, in which the film web being conveyed onto the winder is pressed against the winder with the aid of a contact roll, thereby reducing the amount of air entrapped during winding. The air-displacing effect of the contact roll lessens with increasing winding speed, however, so that a compromise must be made between increasing the winding speed and minimizing the entrapment of air. The whole phenomenology of entrapped air under special consideration of the dependence of entrapped air on the contact roll pressure against the winder is the object of research and development.
It has also been suggested to perform the entire winding procedure in a vaccuum in order to solve the problem of air entrapment. The huge financial expenditure required for vacuum winding, however, speaks against the realization of this suggestion.
The object of the invention is to improve the process described at the outset, and to further develop an apparatus for winding a film web in such a way, that the entrapped air is considerably reduced with little technical expenditure.